A wetted wall cyclone is a device that delivers hydrosol in a single stage from which real-time detection of airborne particles can be readily achieved. This dissertation presents the design, development, and characterization of a family of wetted wall bioaerosol cyclone concentrators that consume very low power and are capable of delivering very small liquid effluent flow rate of highly-concentrated hydrosol. The aerosol-to-aerosol penetration cutpoint for the cyclones is about 1µm. The aerosol-tohydrosol collection efficiency for the 1250 L/min cyclone is above 90% for particle sizes greater than 2 µm at the 1 mL/min liquid effluent flow rate. The aerosol-to-hydrosol collection efficiency for the 100 L/min cyclone is above 85% for particle sizes larger than 2 µm at the 0.1 mL/min liquid effluent flow rate when it is operated at air flow-rate of 100 L/min. The pressure drop across the 1250 L/min and 100 L/min cyclones are approximately 22 inches of water and about 6.4 inches of water, respectively. A study, based on the empirically obtained aerosol-to-aerosol collection efficiency, was conducted to develop a performance modeling correlation that enables prediction of the aerosol performance as a function of the Reynolds number and Stokes number. Since the Reynolds number and Stokes number govern the particle motions in the cyclone, the aerosol performance could be expressed in terms of the Reynolds number and Stokes number. By testing the three cyclones (100, 300, and 1250 L/min cyclones) with several different air flow rates, the aerosol-to-aerosol collection efficiencies for wide range of the Reynolds numbers (3,500 < Re < 30,000) were able to be obtained. Performance modeling correlations for wetted wall cyclones show that the aerosol-toaerosol collection efficiency in the cyclone can be well predicted by the Reynolds number and Stokes number.

A wetted wall cyclone using an airblast atomizer upstream of the inlet was designed as an improvement of a wetted wall cyclone developed by White et al. in 1975, which uses liquid injection through a port on the wall of the cyclone inlet. In the course of this project, many changes to different aspects of the White-type cyclone design and operation were considered. These included inlet configuration, liquid delivery, porous media, surface finishes and coatings, outlet skimmer design, and cyclone body length. The final airblast atomizer cyclone (AAC) design considered has an aerosol-to-hydrosol collection efficiency cut-point of 1.6 µm with collection efficiencies at 2 and 3 µm of 65% and 85%, respectively. The efficiency reported for the White-type cyclone for single Bacillus globigii spores that have a particle size of about 1 µm was approximately 81.8%. The aerosol-to-aerosol transmission efficiency for the AAC configuration was found to be approximately 50% for 1 µm diameter particles as compared with 70 – 100% for the White-type cyclone. A time response test was performed in which the White-type (ca. 2003) cyclone had an initial response of 3 minutes for a condition where there was no liquid carryover through the cyclone outlet and 8 minutes on average with hydrosol carryover. The decay response of the White-type cyclone was 1.25 minutes for non-liquid carryover conditions. The AAC had an initial response of 2.75 minutes and a decay response of 2.5 minutes. The shortened version of the AAC had an initial response of 1.5 minutes and a decay response of 1.25 minutes. There was no liquid carryover observed for any tests of this cyclone configuration. Power consumption tests were performed comparing pressure drops across different variations of White-type cyclones (circa 2003 and 1999) including a variation with an electrical discharge machined (EDM) inlet profile, that reduces the pressure drop at a nominal air flowrate of 780 L/min from 18 inH2O for the basic White-type cyclone (ca. 2003) to 16 inH2O with use of the EDM inlet. Two different variations of White-type cyclones were found to have pressure drops of 25 inH2O and 18 inH2O at an air flowrate of 780 L/min.

A two -stage circumferential slot virtual impactor aerosol concentrator system has been developed that is designed for nominal operational conditions of a 2 μm AD cutpoint, an aerosol inflow to the first stage of 100 L/min and a minor flow rate from the second stage of 1 L/min. Each unit was tested separately before being combined in the system. However, because of high inter-stage losses, a sheath air system was inserted between the two stages, wherein a small amount of air was injected into the apex of a cone placed on top of the second stage. The sheath air displaced the stagnation point at the apex of the cone and redirected particles into the sampling zone of the second stage unit. The cutpoint particle size of the system was 2.5 μm AD at the nominal flow rate. The dynamic range (ratio of upper limit to the lower limit of aerodynamic particle diameter associated with transmission efficiencies of 50%) was 5.4, and the largest particle size for which the transmission was at least 50% is 13.6 μm AD. When run at 67 L/min, the cutpoint is 4 μm AD and the dynamic range is 3.75; at 150 L/min the cutpoint is 2.05 μm AD and the dynamic range is not less than 4.74. The pressure drop across the system is 685 Pa (2.75 in. H2O). This yields an ideal power consumption of 0.77 watts.

A two -stage circumferential slot virtual impactor aerosol concentrator system has been developed that is designed for nominal operational conditions of a 2 μm AD cutpoint, an aerosol inflow to the first stage of 100 L/min and a minor flow rate from the second stage of 1 L/min. Each unit was tested separately before being combined in the system. However, because of high inter-stage losses, a sheath air system was inserted between the two stages, wherein a small amount of air was injected into the apex of a cone placed on top of the second stage. The sheath air displaced the stagnation point at the apex of the cone and redirected particles into the sampling zone of the second stage unit. The cutpoint particle size of the system was 2.5 μm AD at the nominal flow rate. The dynamic range (ratio of upper limit to the lower limit of aerodynamic particle diameter associated with transmission efficiencies of 50%) was 5.4, and the largest particle size for which the transmission was at least 50% is 13.6 μm AD. When run at 67 L/min, the cutpoint is 4 μm AD and the dynamic range is 3.75; at 150 L/min the cutpoint is 2.05 μm AD and the dynamic range is not less than 4.74. The pressure drop across the system is 685 Pa (2.75 in. H2O). This yields an ideal power consumption of 0.77 watts.

No description available.

Two experimental configurations of linear slot nozzle virtual impactors were constructed and experimentally investigated for use as bioaerosol concentrators. In one configuration, the Linear Slot Virtual Impactor (LSVI), the nozzle was a straight slot having a length of 89 mm (3.5"). In the second configuration, the Circumferential Slot Virtual Impactor (CSVI), the nozzle was curvilinear following a circular path having a diameter of 152.4 mm (6.0") and the resulting total slot length was 479 mm (18.8"). Multiple prototypes of the two configurations were constructed having nozzle widths that varied from 0.508 mm (0.015") to 0.203 mm (0.008"). Optical and physical measurements were made of the nozzle dimensions in the critical region of the virtual impactor units. For the LSVI units the misalignment between the acceleration nozzle and the receiver nozzle was measured between 6 µm (0.00025") and 29 µm (0.00114"). This represented a range of 2% to 10% misalignment relative to the acceleration nozzle width. The CSVI Unit 1 and 2 misalignments were measured to be 15 µm (0.00061") and 9 µm (0.00036"), or 10% and 1.8% relative misalignment, respectively. The virtual impactors were tested with liquid and solid monodisperse aerosol particles. For operation at flow rate conditions predicted from the literature to produce a cutpoint of 0.8 µm AD, an acoustic resonance was observed, corresponding to significant nozzle wall losses of particles and an absence of normal particle separation in the virtual impactor. The onset of the resonance phenomenon was observed to begin at a nozzle Reynolds number of approximately 500 for the LSVI configuration, and 300 for the CSVI configuration. For flow rates just below the onset of resonance, normal virtual impactor behavior was observed. The value of Stk50 was 0.58 for both devices, corresponding to a particle cutpoint size of 1.1 µm AD for the LSVI configuration and 2.2 µm AD for the CSVI. The collection efficiency was greater than 72% for all particle sizes larger than twice the cutpoint up to the largest particle size tested (≈ 10 µm AD). The peak collection efficiency for both concentrators was greater than 95%.

A modified wetted-wall cyclone using different methods of water injection techniques upstream of the inlet was designed as an improvement to a wetted-wall cyclone developed by White, which uses liquid injection through a port on the wall of the cyclone inlet. The new cyclone has a high aerosol sampling flow rate (1250 L/min) and maintains constant cut-point with the modified White-type cyclone along with greater collection efficiency, lower time response, and reduced pressure drop. The final air-blast atomizer cyclone (AAC2.1a) design considered has an aerosol-tohydrosol collection efficiency cut-point of 1.3 mm with collection efficiencies at 1 and 2 mm of 39.9% and 86%, respectively. The efficiency reported for the modified White-type cyclone for particle sizes of 1 and 2 mm was 40.5% and 76.3%, respectively, under no water bypass conditions. The aerosol-to-aerosol transmission efficiency for the AAC2.1a configuration was found to be approximately 53.7% for 1 mm diameter particles as compared with 67.2% for the modified White-type cyclone. Dry and wet time response tests were performed in which the modified White-type cyclone had an initial response of 2.5 minutes for a wet start and 1 minute for a dry start for a condition where there was no liquid carryover through the cyclone outlet. The rise time for AAC2.1a cyclone under dry and wet start conditions was 0.5 minutes and 1.3 minutes, respectively. The decay response of the modified White-type cyclone was 1.1 minutes for a wet start and 1.2 minutes for a dry start. The corresponding numbers for AAC2.1a cyclone were 1.4 minutes for a dry start and 1 minute for a wet start condition. Off design tests were run at approximately ±10% air flow rates to see the effect on cyclone performance. It was seen that at a 10% higher flow rate (1350 L/min) the efficiency was 54.3%. At a 10% lower flow rate (1125 L/min) the efficiency was 33.7% as compared with an efficiency of 39.9% at 1250 L/min for 1.0 mm PSL particles. It was found that at a water input of 0.8 mL/min the efficiency reduced to 79.3% as compared to 86% at an input flow rate of 1.6 mL/min for 2 mm size PSL.

Zugl.: Berlin, Freie Universiẗat, Diss., 2008.

Zugl.: Berlin, Freie Universiẗat, Diss., 2008.

Recent studies have shown that Ebola virus can persist in wastewater, and the potential for the virus to be aerosolized and pose a risk of inhalation exposure has not been evaluated. We considered this risk for three wastewater systems: toilets, a lab-scale model of an aeration basin, and a lab-scale model of converging sewer pipes. We measured the aerosol size distribution generated by each system, spiked Ebola virus surrogates into each system, and determined the emission rate of viruses into the air. While the number of aerosols released ranged from 105 to 107 per flush from the toilets or per minute from the lab-scale models, the total volume of aerosols generated by these systems was ~10-8 to 10-7 mL per flush or per minute in all cases. The Ebola virus surrogates MS2 and Phi6, spiked into toilets at an initial concentration of 107 PFU mL-1, were not detected in air after flushing. Airborne concentrations of MS2 and Phi6 were ~20 PFU L-1 and ~0.1 PFU L-1, respectively, associated with the aeration basin and sewer models. This corresponds to emission rates of 547 PFU min-1 and 3.8 PFU min-1 of MS2 and Phi6, respectively, for the aeration basin and 79 PFU min-1 and 0.3 PFU min-1 for the sewer model. Since information on the aerosolization of Ebola virus is quite limited, these emission rates can greatly help inform risk assessment of inhalation exposure to Ebola virus. / Master of Science